Expand.
Answer: We expand the parentheses using the distributive property : $ A(B+C+D)= A\cdot B+ A\cdot C+ A\cdot D$ We can also think about the problem using an area model: $-m^3$ $m^2$ $3m$ $m$ Here's how the solution goes, algebraically: $\begin{aligned} &\phantom{=}{m}(-m^3+m^2+3m) \\\\ &={m}(-m^3)+{m}(m^2)+{m}(3m) \\\\ &=-m^4+m^3+3m^2 \end{aligned}$ Here's how the solution looks in terms of the area model: $-m^4$ $m^3$ $3m^2$ $-m^3$ $m^2$ $3m$ $m$ In conclusion, $m(-m^3+m^2+3m)=-m^4+m^3+3m^2$